1. Field of the Invention
The present invention relates to a pellicle for lithography comprising a film used as a dust-preventing cover for a photomask or a reticle. More particularly it relates to a pellicle that is used in lithography adapted for manufacture of semiconductor devices, such as, LSI and VLSI based on the exposure method wherein a light having a wave length of 500 nm or shorter is generally employed.
In the manufacture of LSI and VLSI semiconductor devices, light is emitted through a mask to a semiconductor wafer to thereby effect patterning on the surface of the wafer. But if the mask is not free of dust, some of the light is absorbed or bent by the dust so that the transferred pattern is deformed or has a rough edge, or the white portion of the transferred pattern is darkened, whereby the dimension quality, and appearance of the pattern are adversely affected.
Therefore, operations of this kind are generally conducted in a clean room; but even so it is not easy to keep the mask free of dust throughout the operation. Hence it has been the usual practice to have the surface of the mask covered with a pellicle which can transmit nearly 100% of the light for lithographical patterning. The pellicle comprises a thin film often made of cellulose nitrate, cellulose acetate, etc. pasted on a frame work.
2. Description of the Prior Art
However, the conventional pellicle film made of cellulose nitrate, cellulose acetate, etc., exhibits a large absorption edge in the short wave length region of the spectrum, such as, 210-400 nm. Generally, it is chemically so unstable that it undergoes yellowing when it absorbs light, so that it cannot be used for VLSI lithography wherein the light emitted is Excimer Laser or i-line ultraviolet light which has a wave length in the range of 210 to 400 nm. Thus, need for a pellicle for lithography that can be used for applications wherein the emitted light has a short wave length, such as, 500 nm or shorter has developed.